Diffractive optical element using polarization rotation grating for in-coupling

ABSTRACT

In an optical display system that includes a waveguide with multiple diffractive optical elements (DOEs), an in-coupling DOE couples light into the waveguide, an intermediate DOE provides exit pupil expansion in a first direction, and an out-coupling DOE provides exit pupil expansion in a second direction and couples light out of the waveguide. The in-coupling DOE is configured with two portions—a first portion includes a grating to rotate a polarization state of in-coupled light while a second portion couples light into the waveguide without modulation of the polarization state. The in-coupled light beams with different polarization states are combined in the waveguide after undergoing total internal reflection. However, as the difference in optical path lengths of the constituent light beams exceeds the coherence length, the combined light has random polarization (i.e., a degree of polarization equal to zero).

BACKGROUND

Diffractive optical elements (DOEs) are optical elements with a periodicstructure that are commonly utilized in applications ranging frombio-technology, material processing, sensing, and testing to technicaloptics and optical metrology. By incorporating DOEs in an optical fieldof a laser or emissive display, for example, the light's “shape” can becontrolled and changed flexibly according to application needs.

SUMMARY

In an optical display system that includes a waveguide with multiplediffractive optical elements (DOEs), an in-coupling DOE couples lightinto the waveguide, an intermediate DOE provides exit pupil expansion ina first direction, and an out-coupling DOE provides exit pupil expansionin a second direction and couples light out of the waveguide. Thein-coupling DOE is configured with two portions—a first portion includesa grating to rotate a polarization state of in-coupled light while asecond portion couples light into the waveguide without modulation ofthe polarization state. The in-coupled light beams with differentpolarization states are combined in the waveguide after undergoing totalinternal reflection. However, as the difference in optical path lengthsof the constituent light beams exceeds the coherence length, thecombined light has random polarization (i.e., a degree of polarizationequal to zero).

The in-coupling DOE with the polarization rotating grating may provideincreased display uniformity in the optical display system by reducingthe “banding” resulting from optical interference that is manifested asdark stripes in the display as randomly polarized light generates weakinterference. Banding may be more pronounced when polymeric materialsare used in volume production of the DOEs to minimize system weight aspolymeric materials may have less optimal optical properties comparedwith other materials such as glass. The in-coupling DOE with thepolarization rotating grating can further enable the optical displaysystem to be more tolerant to variations—such as variations inthickness, surface roughness, and grating geometry—that may not bereadily controlled during manufacturing, particularly since suchvariations are in the submicron range. The in-coupling DOE with thepolarization rotating grating can also improve in-coupling efficiency byreducing back-coupling that is caused by the reciprocity of lightpropagation.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter. Furthermore, the claimed subject matter is not limited toimplementations that solve any or all disadvantages noted in any part ofthis disclosure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an illustrative near eye display systemwhich may incorporate the diffractive optical elements (DOEs) with apolarization rotation grating;

FIG. 2 shows propagation of light in a waveguide by total internalreflection;

FIG. 3 shows a view of an illustrative exit pupil expander;

FIG. 4 shows a view of the illustrative exit pupil expander in which theexit pupil is expanded along two directions;

FIG. 5 shows an illustrative arrangement of three DOEs;

FIG. 6 shows a profile of a portion of an illustrative diffractiongrating that has straight gratings;

FIG. 7 shows an asymmetric profile of a portion of an illustrativediffraction grating that has slanted gratings;

FIG. 8 shows an illustrative in-coupling grating through which light isback-coupled out of a waveguide;

FIG. 9 shows an illustrative in-coupling grating having a portion thatis configured to rotate a polarization state of incident light;

FIGS. 10-13 show various illustrative 2D gratings;

FIG. 14 shows an illustrative arrangement for DOE fabrication using amask that moves relative to a substrate

FIG. 15 shows an illustrative method;

FIG. 16 is a pictorial view of an illustrative example of a virtualreality or mixed reality head mounted display (HMD) device;

FIG. 17 shows a block diagram of an illustrative example of a virtualreality or mixed reality HMD device; and

FIG. 18 shows a block diagram of an illustrative electronic device thatincorporates an exit pupil expander.

Like reference numerals indicate like elements in the drawings. Elementsare not drawn to scale unless otherwise indicated.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of an illustrative near eye display system100 which may incorporate one or more diffractive optical elements(DOEs) that use a polarization rotation grating for in-coupling. Neareye display systems are frequently used, for example, in head mounteddisplay (HMD) devices in industrial, commercial, and consumerapplications. Other devices and systems may also use DOEs withpolarization rotation gratings, as described below. The near eye displaysystem 100 is intended as an example that is used to illustrate variousfeatures and aspects, and the present DOEs are not necessarily limitedto near eye display systems.

System 100 may include an imager 105 that works with an optical system110 to deliver images as a virtual display to a user's eye 115. Theimager 105 may include, for example, RGB (red, green, blue) lightemitting diodes (LEDs), LCOS (liquid crystal on silicon) devices, OLED(organic light emitting diode) arrays, MEMS (micro-electro mechanicalsystem) devices, or any other suitable displays or micro-displaysoperating in transmission, reflection, or emission. The imager 105 mayalso include mirrors and other components that enable a virtual displayto be composed and provide one or more input optical beams to theoptical system. The optical system 110 can typically include magnifyingoptics 120, pupil forming optics 125, and one or more waveguides 130.

In a near eye display system the imager does not actually shine theimages on a surface such as a glass lens to create the visual displayfor the user. This is not feasible because the human eye cannot focus onsomething that is that close. Indeed, rather than create a visible imageon a surface, the near eye display system 100 uses the pupil formingoptics 125 to form a pupil and the eye 115 acts as the last element inthe optical chain and converts the light from the pupil into an image onthe eye's retina as a virtual display.

The waveguide 130 facilitates light transmission between the imager andthe eye. One or more waveguides can be utilized in the near eye displaysystem because they are transparent and because they are generally smalland lightweight (which is desirable in applications such as HMD deviceswhere size and weight is generally sought to be minimized for reasons ofperformance and user comfort). For example, the waveguide 130 can enablethe imager 105 to be located out of the way, for example, on the side ofthe head, leaving only a relatively small, light, and transparentwaveguide optical element in front of the eyes. In one implementation,the waveguide 130 operates using a principle of total internalreflection, as shown in FIG. 2, so that light can be coupled among thevarious optical elements in the system 100.

FIG. 3 shows a view of an illustrative exit pupil expander (EPE) 305.EPE 305 receives an input optical beam from the imager 105 throughmagnifying optics 120 to produce one or more output optical beams withexpanded exit pupil in one or two dimensions relative to the exit pupilof the imager (in general, the input may include more than one opticalbeam which may be produced by separate sources). The expanded exit pupiltypically facilitates a virtual display to be sufficiently sized to meetthe various design requirements of a given optical system, such as imageresolution, field of view, and the like, while enabling the imager andassociated components to be relatively light and compact.

The EPE 305 is configured, in this illustrative example, to supportbinocular operation for both the left and right eyes. Components thatmay be utilized for stereoscopic operation such as scanning mirrors,lenses, filters, beam splitters, MEMS devices, or the like are not shownin FIG. 3 for sake of clarity in exposition. The EPE 305 utilizes twoout-coupling gratings, 310L and 310R that are supported on a waveguide330 and a central in-coupling grating 340. The in-coupling andout-coupling gratings may be configured using multiple DOEs, asdescribed in the illustrative example below. While the EPE 305 isdepicted as having a planar configuration, other shapes may also beutilized including, for example, curved or partially spherical shapes,in which case the gratings disposed thereon would be non-co-planar.

As shown in FIG. 4, the EPE 305 may be configured to provide an expandedexit pupil in two directions (i.e., along each of a first and secondcoordinate axis). As shown, the exit pupil is expanded in both thevertical and horizontal directions. It may be understood that the terms“direction,” “horizontal,” and “vertical” are used primarily toestablish relative orientations in the illustrative examples shown anddescribed herein for ease of description. These terms may be intuitivefor a usage scenario in which the user of the near eye display device isupright and forward facing, but less intuitive for other usagescenarios. The listed terms are not to be construed to limit the scopeof the configurations (and usage scenarios therein) of DOEs withpolarization rotation gratings.

FIG. 5 shows an illustrative arrangement 500 of three DOEs that may beused as part of a waveguide to provide in-coupling and expansion of theexit pupil in two directions. Each DOE is an optical element comprisinga periodic structure that can modulate various properties of light in aperiodic pattern such as the direction of optical axis, optical pathlength, and the like. The first DOE, DOE 1 (indicated by referencenumeral 505), is configured to couple the beam from the imager into thewaveguide. As described in more detail below, DOE 1 is configured withtwo parts or portions—one portion 510 provides polarization rotation toin-coupled incident light and another portion 515 provides no rotation.The second DOE, DOE 2 (520), expands the exit pupil in a first directionalong a first coordinate axis, and the third DOE, DOE 3 (525), expandsthe exit pupil in a second direction along a second coordinate axis andcouples light out of the waveguide. The angle ρ is a rotation anglebetween the periodic lines of DOE 2 and DOE 3 as shown. DOE 1 thusfunctions as an in-coupling grating and DOE 3 functions as anout-coupling grating while expanding the pupil in one direction. DOE 2may be viewed as an intermediate grating that functions to couple lightbetween the in-coupling and out-coupling gratings while performing exitpupil expansion in the other direction. Using such intermediate gratingmay eliminate a need for conventional functionalities for exit pupilexpansion in an EPE such as collimating lenses.

Some near eye display system applications, such as those using HMDdevices for example, can benefit by minimization of weight and bulk. Asa result, the DOEs and waveguides used in an EPE may be fabricated usinglightweight polymers. Such polymeric components can support design goalsfor size, weight, and cost, and generally facilitate manufacturability,particularly in volume production settings. However, polymeric opticalelements generally have lower optical resolution relative to heavierhigh quality glass. Such reduced optical resolution and the waveguide'sconfiguration to be relatively thin for weight savings and packagingconstraints within a device can result in optical interference thatappears as a phenomenon referred to as “banding” in the display. Theoptical interference that results in banding arises from lightpropagating within the EPE that has several paths to the same location,in which the optical path lengths differ.

The banding is generally visible in the form of dark stripes whichdecrease optical uniformity of the display. Their location on thedisplay may depend on small nanometer-scale variations in the opticalelements including the DOEs in one or more of thickness, surfaceroughness, or grating geometry including grating line width, angle, fillfactor, or the like. Such variation can be difficult to characterize andmanage using tools that are generally available in manufacturingenvironments, and particularly for volume production. Conventionalsolutions to reduce banding include using thicker waveguides which canadd weight and complicate package design for devices and systems. Othersolutions use pupil expansion in the EPE in just one direction which canresult in a narrow viewing angle and heightened sensitivity to naturaleye variations among users.

By comparison, when one or more of the DOEs 505, 520, and 525 (FIG. 5)are configured with gratings that have an asymmetric profile, bandingcan be reduced even when the DOEs are fabricated from polymers and thewaveguide 130 (FIG. 1) is relatively thin. FIG. 6 shows a profile ofstraight (i.e., non-slanted) grating features 600 (referred to asgrating bars, grating lines, or simply “gratings”), that are formed in asubstrate 605. By comparison, FIG. 7 shows grating features 700 formedin a substrate 705 that have an asymmetric profile. That is, thegratings may be slanted (i.e., non-orthogonal) relative to a plane ofthe waveguide. In implementations where the waveguide is non-planar,then the gratings may be slanted relative to a direction of lightpropagation in the waveguide. Asymmetric grating profiles can also beimplemented using blazed gratings, or echelette gratings, in whichgrooves are formed to create grating features with asymmetric triangularor sawtooth profiles.

In FIGS. 6 and 7, the grating period is represented by d, the gratingheight by h, bar width by c, and the filling factor by f, where f=c/d.The slanted gratings in FIG. 7 may be described by slant angles α₁ andα₂. In one exemplary embodiment, for a DOE, d=390 nm, c=d/2, h=300 nm,α₁=α₂=45 degrees, f=0.5, and the refractive index of the substratematerial is approximately 1.71. In other implementations, ranges ofsuitable values may include d=250 nm-450 nm, h=200 nm-400 nm, f=0.3-0.0,and α₁=30-50 degrees, with refractive indices of 1.7 to 1.9. In anotherexemplary embodiment, DOE 2 is configured with portions that haveasymmetric profiles, while DOE 1 and DOE 3 are configured withconventional symmetric profiles using straight gratings.

By slanting the gratings in one or more of the DOEs 505, 520, and 525,banding can be reduced to increase optical uniformity while enablingmanufacturing tolerances for the DOEs to be less strict, as comparedwith using the straight grating features shown in FIG. 6 for the samelevel of uniformity. That is, the slanted gratings shown in FIG. 7 aremore tolerant to manufacturing variations noted above than the straightgratings shown in FIG. 6, for comparable levels of optical performance(e.g., optical resolution and optical uniformity).

Optical resolution can also be increased in the EPE 305 (FIG. 3) byrotating the polarization of one part of the input pupil and combiningit with a non-rotated part. To illustrate this technique, a discussionof a conventionally configured in-coupling grating is first presented.FIG. 8 shows an edge view of an illustrative conventional in-couplinggrating 805 through which some amount of incident light 810 exits thewaveguide 830 on the side of incidence as back-coupled light 840. Theback-coupling occurs because the coupled light undergoes total internalreflection and meets the in-coupling grating 805 and is coupled out ofthe waveguide through reciprocal light propagation. Back-coupling canreduce the efficiency of the in-coupling grating 805 in coupling lightinto the optical system. In addition, the in-coupled light using theconventional in-coupling grating 805 can generate visible banding indownstream optical elements as a result of multiple optical paths to agiven point in the system in which the path length differences are lessthan the coherence length (i.e., a propagation distance over which thelight may be considered coherent).

By comparison, FIG. 9 shows an edge view of an illustrative in-couplinggrating 900 that has distinct parts or portions in which a first portion905 provides polarization rotation to incident light and a secondportion 910 does not modulate the polarization of incident light. Asdiscussed above, in-coupling grating 900 may be used in someimplementations for DOE 1 in the DOE arrangement 500 shown in FIG. 5 anddescribed in the accompanying text. As shown, an incident beam iscoupled into the waveguide 930 by the first portion 905 of thein-coupling grating 900. In this example, the incident beam is a TEpolarized beam 915, but incident light could alternatively be TMpolarized, or be left or right hand circularly polarized. The firstportion 905 of the in-coupling grating rotates the polarization of thein-coupled TE polarized beam to a TM polarized beam 920.

When the TM polarized beam 920 undergoes total internal reflection inthe waveguide 930 and meets the second portion 910 of the in-couplingDOE 900 the TM polarized beam is not coupled out of the waveguide asback-coupled light because the rotated polarization limits interactionwith the second portion 910 of the in-coupling grating. This can help toreduce back-coupling in the optical system and thus increase overallin-coupling efficiency.

Another incident TE polarized beam 925 is in-coupled by the secondportion 910 of the in-coupling DOE 900 without modulating thepolarization. In the waveguide 930, the beams 920 and 925 with differentpolarizations combine after undergoing total internal reflection. Thecombined beam 935 is unpolarized (i.e., has random polarization in whichthe degree of polarization is equal to zero). The randomly polarizedlight generates relatively weak interference in the downstream DOEs,particularly, for example, in the intermediate DOE 2 (element 520 inFIG. 5) where there are multiple optical paths to any given point andthe path length differences are small (i.e., less than the coherencelength).

The polarization rotating portion 905 of the in-coupling DOE 900 may beimplemented using multi-dimensional gratings such as two-dimensional(2D) gratings having periodicity in two different directions. Thefilling ratio of the grating structure can be varied to control thedegree of polarization modulation. Alternatively, other suitabletechnologies may also be employed for polarization rotation such as thinfilm polarizing filters. A 2D grating may utilize a variety ofstructures, contours, surface relief features and the like that areperiodic in two dimensions according to the needs of a particularimplementation.

For example, FIGS. 10-13 depict various illustrative 2D gratings asrespectively indicated by reference numerals 1005, 1105, 1205 and 1305.The 2D gratings in the drawings are intended to be illustrative and notlimiting, and it is contemplated that variations from the 2D gratingsshown may also be utilized. Gratings may include symmetric and/orasymmetric features including slanted gratings (i.e., gratings havingwalls that are non-orthogonal according to one or more predeterminedangles to a plane of the waveguide) and blazed gratings (i.e., gratingshaving asymmetric triangular or sawtooth profiles) in some cases.Various suitable surface relief contours/elements/features, fillingfactors, grating periods, and grating dimensions can also be utilizedand implemented to control various optical properties andcharacteristics according to the needs of a particular implementation.

FIG. 10 shows a 2D grating 1005 that includes quadrangular elements thatproject from a substrate. The quadrangular elements can also beconfigured to be asymmetric such as being slanted or blazed.Non-quadrangular three-dimensional geometries (both symmetric andasymmetric) may also be utilized for a 2D grating including, forexample, cylindrical elements, polygonal elements, elliptical elements,or the like. For example, FIG. 11 shows a 2D grating 1105 that includespyramidal elements, and FIG. 12 shows a 2D grating 1205 that includeselements that have a blazed profile in each of the x and z directions.Gratings may also have elements with curved profiles, as shown in theillustrative 2D grating 1305 in FIG. 13.

FIG. 14 shows an illustrative arrangement for DOE fabrication using amask 1405 that moves relative to a photosensitive grating substrate 1410within an enclosure 1415. A reactive ion etching plasma 1420 is used toadjust the thickness of the etching on the grating substrate at variouspositions by moving the substrate relative to the mask using, forexample, a computer-controller stepper functionality or other suitablecontrol system. In an illustrative example, the etching may be performedusing a reactive ion beam etching (RIBE). However, other variations ofion beam etching may be utilized in various implementations including,for example, such as magnetron reactive ion etching (MRIE), high densityplasma etching (HDP), transformer coupled plasma etching (TCP),inductively coupled plasma etching (ICP), and electron resonance plasmaetching (ECR). In some implementations, the substrate holder 1408 may beconfigured to rotate the grating substrate 1410 about an axis relativeto a reactive ion etching plasma source 1420. Exposure to the plasma maybe used, for example, to adjust the thickness and orientation of theetching on the grating substrate at various positions by angling thesubstrate relative to the source 1420.

By controlling the exposure of the substrate to the plasma through themask aperture, grating depth can be varied as a function of positionover the extent of the substrate to thereby enable various gratingprofiles to be incorporated on the substrate. The resultingmicrostructure on the substrate may be replicated for mass production ina lightweight polymer material using one of cast-and-cure, embossing,compression molding, or compression injection molding, for example.

FIG. 15 is a flowchart of an illustrative method 1500. Unlessspecifically stated, the methods or steps shown in the flowchart anddescribed in the accompanying text are not constrained to a particularorder or sequence. In addition, some of the methods or steps thereof canoccur or be performed concurrently and not all the methods or steps haveto be performed in a given implementation depending on the requirementsof such implementation and some methods or steps may be optionallyutilized.

In step 1505, light is received at an in-coupling DOE. The in-couplingDOE is disposed in an EPE and interfaces with the downstreamintermediate DOE that is disposed in the EPE. The in-coupling DOEincludes a polarization rotating portion and a portion that performs nopolarization modulation. In step 1510, the exit pupil of the receivedlight is expanded along a first coordinate axis in the intermediate DOE.In step 1515, the exit pupil is expanded in an out-coupling DOE whichoutputs light with an expanded exit pupil relative to the received lightat the in-coupling DOE along the first and second coordinate axes instep 1520. The intermediate DOE is configured to interface with adownstream out-coupling DOE. In some implementations, the out-couplingDOE may be apodized with shallow gratings that are configured to beeither straight or slanted.

DOEs with polarization rotating grating portions for in-coupling may beincorporated into a display system that is utilized in a virtual ormixed reality display device. Such device may take any suitable form,including but not limited to near eye devices such as an HMD device. Asee-through display may be used in some implementations while an opaque(i.e., non-see-through) display using a camera-based pass-through oroutward facing sensor, for example, may be used in otherimplementations.

FIG. 16 shows one particular illustrative example of a see-through,mixed reality or virtual reality display system 1600, and FIG. 17 showsa functional block diagram of the system 1600. Display system 1600comprises one or more lenses 1602 that form a part of a see-throughdisplay subsystem 1604, such that images may be displayed using lenses1602 (e.g. using projection onto lenses 1602, one or more waveguidesystems incorporated into the lenses 1602, and/or in any other suitablemanner). Display system 1600 further comprises one or moreoutward-facing image sensors 1606 configured to acquire images of abackground scene and/or physical environment being viewed by a user, andmay include one or more microphones 1608 configured to detect sounds,such as voice commands from a user. Outward-facing image sensors 1606may include one or more depth sensors and/or one or more two-dimensionalimage sensors. In alternative arrangements, as noted above, a mixedreality or virtual reality display system, instead of incorporating asee-through display subsystem, may display mixed reality or virtualreality images through a viewfinder mode for an outward-facing imagesensor.

The display system 1600 may further include a gaze detection subsystem1610 configured for detecting a direction of gaze of each eye of a useror a direction or location of focus, as described above. Gaze detectionsubsystem 1610 may be configured to determine gaze directions of each ofa user's eyes in any suitable manner. For example, in the illustrativeexample shown, a gaze detection subsystem 1610 includes one or moreglint sources 1612, such as infrared light sources, that are configuredto cause a glint of light to reflect from each eyeball of a user, andone or more image sensors 1614, such as inward-facing sensors, that areconfigured to capture an image of each eyeball of the user. Changes inthe glints from the user's eyeballs and/or a location of a user's pupil,as determined from image data gathered using the image sensor(s) 1614,may be used to determine a direction of gaze.

In addition, a location at which gaze lines projected from the user'seyes intersect the external display may be used to determine an objectat which the user is gazing (e.g. a displayed virtual object and/or realbackground object). Gaze detection subsystem 1610 may have any suitablenumber and arrangement of light sources and image sensors. In someimplementations, the gaze detection subsystem 1610 may be omitted.

The display system 1600 may also include additional sensors. Forexample, display system 1600 may comprise a global positioning system(GPS) subsystem 1616 to allow a location of the display system 1600 tobe determined. This may help to identify real world objects, such asbuildings, etc. that may be located in the user's adjoining physicalenvironment.

The display system 1600 may further include one or more motion sensors1618 (e.g., inertial, multi-axis gyroscopic, or acceleration sensors) todetect movement and position/orientation/pose of a user's head when theuser is wearing the system as part of a mixed reality or virtual realityHMD device. Motion data may be used, potentially along with eye-trackingglint data and outward-facing image data, for gaze detection, as well asfor image stabilization to help correct for blur in images from theoutward-facing image sensor(s) 1606. The use of motion data may allowchanges in gaze location to be tracked even if image data fromoutward-facing image sensor(s) 1606 cannot be resolved.

In addition, motion sensors 1618, as well as microphone(s) 1608 and gazedetection subsystem 1610, also may be employed as user input devices,such that a user may interact with the display system 1600 via gesturesof the eye, neck and/or head, as well as via verbal commands in somecases. It may be understood that sensors illustrated in FIGS. 16 and 17and described in the accompanying text are included for the purpose ofexample and are not intended to be limiting in any manner, as any othersuitable sensors and/or combination of sensors may be utilized to meetthe needs of a particular implementation. For example, biometric sensors(e.g., for detecting heart and respiration rates, blood pressure, brainactivity, body temperature, etc.) or environmental sensors (e.g., fordetecting temperature, humidity, elevation, UV (ultraviolet) lightlevels, etc.) may be utilized in some implementations.

The display system 1600 can further include a controller 1620 having alogic subsystem 1622 and a data storage subsystem 1624 in communicationwith the sensors, gaze detection subsystem 1610, display subsystem 1604,and/or other components through a communications subsystem 1626. Thecommunications subsystem 1626 can also facilitate the display systembeing operated in conjunction with remotely located resources, such asprocessing, storage, power, data, and services. That is, in someimplementations, an HMD device can be operated as part of a system thatcan distribute resources and capabilities among different components andsubsystems.

The storage subsystem 1624 may include instructions stored thereon thatare executable by logic subsystem 1622, for example, to receive andinterpret inputs from the sensors, to identify location and movements ofa user, to identify real objects using surface reconstruction and othertechniques, and dim/fade the display based on distance to objects so asto enable the objects to be seen by the user, among other tasks.

The display system 1600 is configured with one or more audio transducers1628 (e.g., speakers, earphones, etc.) so that audio can be utilized aspart of a mixed reality or virtual reality experience. A powermanagement subsystem 1630 may include one or more batteries 1632 and/orprotection circuit modules (PCMs) and an associated charger interface1634 and/or remote power interface for supplying power to components inthe display system 1600.

It may be appreciated that the display system 1600 is described for thepurpose of example, and thus is not meant to be limiting. It is to befurther understood that the display device may include additional and/oralternative sensors, cameras, microphones, input devices, outputdevices, etc. than those shown without departing from the scope of thepresent arrangement. Additionally, the physical configuration of adisplay device and its various sensors and subcomponents may take avariety of different forms without departing from the scope of thepresent arrangement.

As shown in FIG. 18, an EPE incorporating one or more DOEs withpolarization rotating grating portions for in-coupling can be used in amobile or portable electronic device 1800, such as a mobile phone,smartphone, personal digital assistant (PDA), communicator, portableInternet appliance, hand-held computer, digital video or still camera,wearable computer, computer game device, specialized bring-to-the-eyeproduct for viewing, or other portable electronic device. As shown, theportable device 1800 includes a housing 1805 to house a communicationmodule 1810 for receiving and transmitting information from and to anexternal device, or a remote system or service (not shown).

The portable device 1800 may also include an image processing module1815 for handling the received and transmitted information, and avirtual display system 1820 to support viewing of images. The virtualdisplay system 1820 can include a micro-display or an imager 1825 and anoptical engine 1830. The image processing module 1815 may be operativelyconnected to the optical engine 1830 to provide image data, such asvideo data, to the imager 1825 to display an image thereon. An EPE 1835using one or more DOEs with polarization rotating grating portions forin-coupling can be optically linked to an optical engine 1830.

An EPE using one or more DOEs with polarization rotating gratingportions for in-coupling may also be utilized in non-portable devices,such as gaming devices, multimedia consoles, personal computers, vendingmachines, smart appliances, Internet-connected devices, and homeappliances, such as an oven, microwave oven, and other appliances, andother non-portable devices.

Various exemplary embodiments of the present diffractive optical elementusing polarization rotation gratings for in-coupling are now presentedby way of illustration and not as an exhaustive list of all embodiments.An example includes an optical system, comprising: a substrate ofoptical material; a first diffractive optical element (DOE) disposed onthe substrate, the first DOE having an input surface and configured asan in-coupling grating to receive one or more optical beams as an input;and a second DOE disposed on the substrate and configured for pupilexpansion of the one or more optical beams along a first direction,wherein at least a portion of the first DOE is configured with apolarization rotating grating.

In another example, the polarization rotating grating is configured as atwo-dimensional grating that is periodic in two different directions. Inanother example, the one or more optical beams received at the first DOEemanate as a virtual image produced by a micro-display or imager. Inanother example, the optical system further includes a third DOEdisposed on the substrate, the third DOE having an output surface andconfigured for pupil expansion of the one or more optical beams along asecond direction, and further configured as an out-coupling grating tocouple, as an output from the output surface, one or more optical beamswith expanded pupil relative to the input. In another example,differences among optical path lengths in the second DOE exceed acoherence length so as to improve display uniformity in the third DOE.

A further example includes an electronic device, comprising: a dataprocessing unit; an optical engine operatively connected to the dataprocessing unit for receiving image data from the data processing unit;an imager operatively connected to the optical engine to form imagesbased on the image data and to generate one or more input optical beamsincorporating the images; and an exit pupil expander, responsive to theone or more input optical beams, comprising a structure on whichmultiple diffractive optical elements (DOEs) are disposed, in which theexit pupil expander is configured to provide one or more output opticalbeams, using one or more of the DOEs, as a near eye virtual display withan expanded exit pupil, and wherein at least one of the DOEs has atleast one portion configured as a polarization rotating grating with aplurality of grating elements that are periodically arranged along firstand second directions that are different from each other.

In another example, the at least one DOE further includes at least oneother portion that is configured to perform no polarization modulationof incident light. In another example, the exit pupil expander providespupil expansion in two directions. In another example, the imagerincludes one of light emitting diode, liquid crystal on silicon device,organic light emitting diode array, or micro-electro mechanical systemdevice. In another example, the imager comprises a micro-displayoperating in one of transmission, reflection, or emission. In anotherexample, the electronic device is implemented in a head mounted displaydevice or portable electronic device. In another example, each of theone or more input optical beams is produced by a corresponding one ormore sources. In another example, the structure is curved or partiallyspherical. In another example, two or more of the DOEs arenon-co-planar.

A further example includes a method, comprising: receiving light at anin-coupling diffractive optical element (DOE) disposed in an exit pupilexpander; expanding an exit pupil of the received light along a firstcoordinate axis in an intermediate DOE disposed in the exit pupilexpander; expanding the exit pupil along a second coordinate axis in anout-coupling DOE disposed in the exit pupil expander; and outputtinglight with an expanded exit pupil relative to the received light at thein-coupling DOE along the first and second coordinate axes using theout-coupling DOE, in which the in-coupling DOE includes gratingsconfigured to provide a periodic contoured surface having a firstperiodicity along a first direction and a second periodicity along asecond direction so as to cause rotation of a polarization state ofoptical beams that are incident on the in-coupling DOE.

In another example, the periodic contoured surface comprises one ofquadrangular elements, cylindrical elements, polygonal elements,elliptical elements, pyramidal elements, curved elements, orcombinations thereof. In another example, the in-coupling DOE, theintermediate DOE, or the out-coupling DOE is formed with a polymer thatis molded from a substrate that is etched using ion beam etching inwhich the substrate has changeable orientation relative to an ion beamsource. In another example, at least a portion of the out-coupling DOEis an apodized diffraction grating having shallow grooves relative tothe in-coupling DOE or the intermediate DOE. In another example, themethod is performed in a near eye display system. In another example,the output light provides a virtual display to a user of the near eyedisplay system.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed:
 1. An optical system, comprising: a substrate ofoptical material; a first diffractive optical element (DOE) disposed onthe substrate, the first DOE having an input surface and configured asan in-coupling grating to receive one or more optical beams as an input;and a second DOE disposed on the substrate and configured for pupilexpansion of the one or more optical beams along a first direction,wherein at least a portion of the first DOE is configured with apolarization rotating grating.
 2. The optical system of claim 1 in whichthe polarization rotating grating is configured as a two-dimensionalgrating that is periodic in two different directions.
 3. The opticalsystem of claim 1 in which the one or more optical beams received at thefirst DOE emanate as a virtual image produced by a micro-display orimager.
 4. The optical system of claim 1 further including a third DOEdisposed on the substrate, the third DOE having an output surface andconfigured for pupil expansion of the one or more optical beams along asecond direction, and further configured as an out-coupling grating tocouple, as an output from the output surface, one or more optical beamswith expanded pupil relative to the input.
 5. The optical system ofclaim 4 in which differences among optical path lengths in the secondDOE exceed a coherence length so as to improve display uniformity in thethird DOE.
 6. An electronic device, comprising: a data processing unit;an optical engine operatively connected to the data processing unit forreceiving image data from the data processing unit; an imageroperatively connected to the optical engine to form images based on theimage data and to generate one or more input optical beams incorporatingthe images; and an exit pupil expander, responsive to the one or moreinput optical beams, comprising a structure on which multiplediffractive optical elements (DOEs) are disposed, in which the exitpupil expander is configured to provide one or more output opticalbeams, using one or more of the DOEs, as a near eye virtual display withan expanded exit pupil, and wherein at least one of the DOEs has atleast one portion configured as a polarization rotating grating with aplurality of grating elements that are periodically arranged along firstand second directions that are different from each other.
 7. Theelectronic device of claim 6 in which the at least one DOE furtherincludes at least one other portion that is configured to perform nopolarization modulation of incident light.
 8. The electronic device ofclaim 6 in which the exit pupil expander provides pupil expansion in twodirections.
 9. The electronic device of claim 6 in which the imagerincludes one of light emitting diode, liquid crystal on silicon device,organic light emitting diode array, or micro-electro mechanical systemdevice.
 10. The electronic device of claim 6 in which the imagercomprises a micro-display operating in one of transmission, reflection,or emission.
 11. The electronic device of claim 6 as implemented in ahead mounted display device or portable electronic device.
 12. Theelectronic device of claim 6 in which each of the one or more inputoptical beams is produced by a corresponding one or more sources. 13.The electronic device of claim 6 in which the structure is curved orpartially spherical.
 14. The electronic device of claim 6 in which twoor more of the DOEs are non-co-planar.
 15. A method, comprising:receiving light at an in-coupling diffractive optical element (DOE)disposed in an exit pupil expander; expanding an exit pupil of thereceived light along a first coordinate axis in an intermediate DOEdisposed in the exit pupil expander; expanding the exit pupil along asecond coordinate axis in an out-coupling DOE disposed in the exit pupilexpander; and outputting light with an expanded exit pupil relative tothe received light at the in-coupling DOE along the first and secondcoordinate axes using the out-coupling DOE, in which the in-coupling DOEincludes gratings configured to provide a periodic contoured surfacehaving a first periodicity along a first direction and a secondperiodicity along a second direction so as to cause rotation of apolarization state of optical beams that are incident on the in-couplingDOE.
 16. The method of claim 15 in which the periodic contoured surfacecomprises one of quadrangular elements, cylindrical elements, polygonalelements, elliptical elements, pyramidal elements, curved elements, orcombinations thereof.
 17. The method of claim 15 in which thein-coupling DOE, the intermediate DOE, or the out-coupling DOE is formedwith a polymer that is molded from a substrate that is etched using ionbeam etching in which the substrate has changeable orientation relativeto an ion beam source.
 18. The method of claim 15 further in which atleast a portion of the out-coupling DOE is an apodized diffractiongrating having shallow grooves relative to the in-coupling DOE or theintermediate DOE.
 19. The method of claim 15 as performed in a near eyedisplay system.
 20. The method of claim 19 in which the output lightprovides a virtual display to a user of the near eye display system.